LED Bonding Wire

3D sketch of LED bonding process

Bonding wire is a critical component in LED packaging (encapsulation) processes to provide electrical interconnection between LED chip and peripheral frame.

 

Most of LED bonding wire is made of high purity (99.99%) gold as gold has many advantages as lead wire. First of all, gold is a good contact metal to conduct heat and electronic. The thermal conductivity of gold is 317 W/mK, close to silver (429W/mK) and copper(401W/mK) however gold lasts much longer as it will not be oxidized easily. Gold is of perfect ductility so it doesn’t easily break even under high tension; Very importantly, gold is highly reflective of light. According to iLUXZ’s experiment result, under the same experimental conditions, LED encapsulations with golden bonding wire produce 3.55% more light (lumen) in average than LED encapsulations with copper wire. 

 

There’re also many alternative materials for LED bonding for cost control purpose. Some LED manufacturers are using copper wire or even alloy wire now to reduce cost. However, compared to gold wire, copper is significantly more prone to corrosion issues, besides, if the compounds are not selected properly, it will result in internal CTE (Coefficient of Thermal Expansion) mismatches with the copper wire bonds that can eventually lead to device failures during thermal cycling.

Some manufacturers are using the golden doped with copper or aluminum to replace the pure golden wire to reduce the cost, however, the alloy wire has the drawback that is  very easily oxidized. The electrical conductivity, thermal conductivity of the oxidized wire will be sharply decreased, and which is harmful to the LED. While, the high purity gold wire is very steady, even under the high current and temperature they can function very well.  

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